import java.util.Scanner;

/**
 * Created With IntelliJ IDEA
 * Description:牛客网: 首页 > 试题广场 > 客似云来
 * <a href="https://www.nowcoder.com/questionTerminal/3549ff22ae2c4da4890e9ad0ccb6150d">...</a>
 * User: DELL
 * Data: 2023-04-27
 * Time: 0:31
 */
public class Main {
    /**
     * 观察题目,本质上就是求斐波那契数列的问题
     * @param args
     */
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while (scanner.hasNext()) {
            int from = scanner.nextInt();
            int to = scanner.nextInt();
            //因为from和to的取值范围为 1<=from<=to<=80
            //因此有可能会超出int类型的取值范围,这里使用long
            long temp1 = 0;
            long temp2 = 1;
            //记住第 from 个斐波那契数
            for (int i = 0; i < from-1; i++) {
                long temp = temp2;
                temp2 = temp1+temp2;
                temp1 = temp;
            }
            long sum = 0;
            for (int i = from; i <= to; i++) {
                sum += temp2;
                long temp = temp2;
                temp2 = temp1+temp2;
                temp1 = temp;
            }
            System.out.println(sum);
        }
    }
}
